Curtis Cheng murder haunts Nick Kaldas

Mr Kaldas was in charge of most of those inside the force's Parramatta headquarters when Mr Cheng, a police accountant, was gunned down by 15-year-old schoolboy Farhad Jabar in October, 2015.

"I have to tell you, I and most senior police lay awake at night thinking could we have done something different, is there something we should have had in place?" he said at a security summit in Canberra on Wednesday.

"If we had people with MP5s (sub-machine guns) standing out the front, would this have happened?"

Australian law enforcement agencies should have a much tougher and more visible presence, Mr Kaldas said, arguing there were many international examples where more heavily-armed police may have saved lives.

He championed the New York approach of deploying heavily-armed tactical officers at unpredictable times and places across the city.

"If you turn up to recce - I won't pick on the Sydney Opera House, but if somebody turns up to have a look at it - and you've got people there who are so physically capable of repelling you it's going to put you off.

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"The message that you want to the send to the bad guys with that visible, overwhelming and robust deterrent is that this city is not going to be an easy target for you."

Mr Kaldas said the days of police carrying truncheons and Tasers were waning.

"We face an enemy that is prepared to kill people and to die in the course of doing that ... the only thing that can stop them is firepower," he said.

"There is a pressing need for consideration of much more powerful firearms being issued to first responders and to police on the street in certain areas at certain times."

This hardline approach must still be intelligence-led and coupled with community engagement, Mr Kaldas said.

He also called for more effective private-public engagement on information sharing and funding for research and resources, as well as a more consistent, unified national approach and international co-operation.

The threats posed by global issues including cyber security and returning foreign fighters were not going away, and national and international security agencies needed to "co-operate or perish".

"I think ISIS will probably be defeated militarily, but I regret to say it probably will not end our problems; in fact I think our threat will probably get worse," Mr Kaldas said.

"There is a string of ever-increasing failed or failing states and each of them has an impact on us in the West in some way."